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Firstly, apologies for a vague title ; I didnt know what to say.

I have a particular pdf (book). However I am having a lot of trouble reading this pdf. The issue is that the background color, which is white, is "too much white or dark white" and the text of the pdf is "too much black or dark black" , which hurts the eyes a lot.

Now with other pdf files, what I normally do is

1) Configure the page color of ocular and set it to some light or medium gray shade which is comfortable

2) Control brightness using xbacklight to further improve reading comfort

However, none of these strategies work . Decreasing the brightness doesnt help because the colors ( as mentioned above) are still too dark. Changing page color for this particular pdf changes only border color of the page, and not of the entire page ; again no use.

So is there something which I can do ?

(Please keep in mind that I am a noob user who doesnt knows much of command lines etc and dont want unnecessary headaches just because I edited a wrong file..etc)

Thank you.

2 Answers 2

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The problem is probably that this pdf is only a "pdf image file". With your cursor can you highlight words, i. e. the actual characters. Or does just draw a box.

Image pdf can have poor image contrast. Whereas if you use OCR (optical character recognition) then each character is distinct from the background, and Okular can set each independently; there by controlling your contrast ratio of light vs. dark.

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    So is there anything I can do to increase the reading comfort of this pdf ? Jan 12, 2015 at 3:36
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Beside the older setting of inverting colors (which might not work on scanned documents anyway), in newer versions of Okular (like 1.9.3) both font and page colors can be edited — and a dark-mode look can be enabled — through a new and rather non-intuitive setting, under Configure Okular - Accessibility - Color mode: Change Dark and Light Colors, by selecting a light color for dark and a dark one for light color option.

enter image description here

Then, for easy access, configure toolbar and add Toggle change color (Icon can be manually added/edited). It works for picture/scanned pages too.

enter image description here

This setting is a bit odd because of the names used.

Depending on the type of pdf, the color of the text (that is, the "Dark Color", meaning font color, which was set to a lighter hue) may change in part the color of the background, which thus becomes lighter than the selection under "Light Color" (meaning background color). This happens rather in some scanned documents, but not in all. It may be related to gray or colored backgrounds, which can be changed as said here.

Other PDF readers that can change both font and page background color of image-based pdf files are the very minimalist Zathura (see this answer) and the full-featured Master PDF Editor (more details in this answer, even more here).

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